Question

Which term of the AP 72, 63, 54, ... is 0?
(a) 8th
(b) 9th
(c) 10th
(d) 11th

Answer 1

(b) 9^th

In the given AP, we have a = 72 and d = (63 - 72) = - 9
Let n^th terms be 0.
Then T_n = 0
⇒ a + (n -1) d = 0
⇒ 72 + (n - 1) ⨯(-9) = 0
⇒ 81 - 9n = 0
⇒ 9n = 81
⇒ n = 9
Hence, the 9^th term is 0.